Signal apparatus



y 21, 1946- D. E. WATTS ETAL 2,400,796

S IGNAL APPARATUS Filed Dec. 29, 1939 SOURCE or curorr ems POTENT/HL I VERSE RESIST/INC'E-CURRENT souuo HEAD f Inventors: ocsm FLOOR D nald E. Watts,

Paul C. Gardner,

TheirAtt orney.

Patented May 21, 1946 2,400,796 SIGNAL APPARATUS Donald E. Watts, Schenectady, and Paul C. Gardiner, Scotia, N. Y., assignors to General Electric Company, a corporation of New York Application December 29, 1939, Serial No. 311,532

3 Claims.

Our invention relates to signal apparatus, and, while not limited thereto, it relates particularly to signal systems such as are used for submarine depth finding.

In such systems commonly a wave generating apparatus, or transmitter, is utilized to supply signal impulses to a translating apparatus, or sound head, which operates to emit sound, or compressional, waves to a distant reflecting surface, which may be the bottom of the sea, or distant object, to be detected, Such waves are refiected from such a surface and are received in the same translating apparatus and are supplied to receiving equipment connected thereto.

One of the objects of our invention is to provide certain improvements in such a system whereby the transmitter and the receiver, which are connected to the same sound head, operate more independently of each other.

Another object of our invention is to provide means to reduce the portion of energy received from a distant reflecting surface which is absorbed or wasted in the transmitting equipment connected to the translating apparatus thereby to increase the response of the receiver to such reflected waves.

A further object of our invention is to provide means to prevent the resonant circuits of the receiver from becoming so excited during transmission of an impulse that, by reason of their persistence of oscillation, their response to the same impulse after reflection from a distant surface is impaired. That is, the transmitted impulse is received from the distant reflecting surface after a short time interval, the duration of which is dependent upon the distance to the reflecting surface, which distance it may be de sired to measure. It is necessary that the resonant circuits of the receiver be capable of producing satisfactory response to the reflected wave after such time interval notwithstanding any eflect produced upon them by the last previous outgoing impulse.

The features of our invention which we believe to be novel are set forth with particularit in the appended claims. Our invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure of the drawing illustrates apparatus embodying our invention.

Referring to the figure, there is shown a transmitter including a balanced oscillator comprising a pair of electron discharge devices 10 and II and an amplifier comprising a pair of electron discharge amplifying devices l2 and I3 transmitting signals through a transformer [4 to a pair of wires l5 and to a sound head 80, which converts the electric wave into a sound wave to be reflected from the ocean floor 8|. There is also connected to the same pair of wires IS a receiver, operating in the same frequency band as the transmitter. This receiver comprises a pair of electron discharge amplifying devices I6 and H connected in balanced relation, a second pair of electron discharge amplifying devices It! and I9, and a glow lamp 20.

The cathodes of the oscillating discharge devices ill and H are connected together and to ground, and the anodes 58 and 59 thereof are supplied with operating potential through an inductance 2| connected between them and through a choke coil 30 connected between the central point of inductance 2| and the positive terminal ofa source 16 of potential, the negative terminal of which is grounded. The inductance 2| is tuned by two parallel sets of four series-connected condensers 22, 23, 24, 25 and 26, 21, 28, 29 connected in shunt thereto. The control grids 60 and 6| of the devices l0 and I l are connected respectively through inductances 3| and 32 and through a common grid resistor 33 to ground. The grid 60 of the device I0 is excited from the tuned circuit b connection to a point between condensers 28 and 29, condenser 29 being connected to the anode -59 of the device II. The grid 6| of the device II is excited from the tuned circuit by connection to a point between condensers 26 and 21. Points between condensers 23 and 24 and between 21 and 28 are grounded. The circuit as described and illustrated is adjusted for oscillation, A switch 34, operated continuously by a rotating cam 82, is arranged to connect the ungrounded terminal of the grid resistor 33 to wire 62 connected to a source of negative grid bias potential, not shown. The switch 34 is opened for a brief interval at each rotation of the cam 82 so that the oscillator operates during repeated'short intervals.

The cathodes of the amplifying devices l2 and I3 are connected together and to ground and the grids 63 and 64 thereof are connected through grid resistors 35 and 36 respectively to points between condensers 22 and 23 and condensers 24 and 25. These points are connected through choke coils 31 and 38 to a common point 65, to which grid bias potential is supplied through a resistor 39 from a source 15 of potential. This bias potential is sufllciently negative so that the discharge devices I2 and I3 are substantially nonconductive in the absence of signals from the oscillator.

The anodes 68 and 61 of the devices I2 and I3 are connected to opposite ends of the primary of the transformer I4, the central point of which is supplied with anode operating potential through a choke coil 40 from a source 11 of potential. This central point is, by-passed to the cathodes of devices I2 and I8 at ground through a condenser 4I. Condensers 42 and 43, connected between the grids 63 and 84 of the devices I2 and I3 and the opposite anodes 31 and 88, respectively, provide neutralization for the amplifying devices.

The primary of a receiver input transformer 44 is coupled to the pair of wires I5 by a pair of coupling condensers 45 and 46. This primary is shunted by a non-linear resistor 41, such as is described in United States Patent No. 1,822,742, issued to K. B. McEachron and which is commonly known as Thyrite. This non-linear resistor has a hyperbolic resistance-current characteristic which can be expressed in the form of a simple hyperbolic equation, as R=CI-, where R is the resistance, I is the density of the current in amperes, C is a constant, and the exponent a is the slope of the curve represented by the equation when plotted with respect to logarithmic coordinates. The exponent a is less than unity and the constant C is in the range between and 600. This material has the peculiar property of reacting substantially instantaneously to an increase or decrease of voltage applied thereacross by a respective decrease or increase of its resistance.

In the choice of this resistance material it is desirable that the exponent a be as small as possible in order that the resistor 41 shall have as small a shunting effect on the receiver input as possible up to a certain voltage level and as large a shunting effect as possible above such level. By suitable choice of the constant C and the size of the resistor 41 it is desirable to make themsistance of resistor 41 such that it remains high up to a voltage level higher than that produced by the sound head 80 in receiving reflected waves and such that above that level it is as greatly reduced as possible in the presence of voltages of the order of those produced by the transmitter. It is desirable that the resistance of the resistor 41 in the presence of low voltages be of the order of the impedance of the input circuit to the discharge devices and I1.

The secondary of the transformer 44 is connected in shunt to a condenser 48 and its center point is by-passed to the cathodes of devices I8 and I1 at ground by a condenser 50. The resistor 41 is eflectively in shunt to the tuned circuit formed by the transformer 44 and the condenser 48. The tuned circuit 44, 48 excites the control grids 68 and 69 of devices I8 and I1 in balanced relation. Bias potential for these grids 68 and 89 is supplied through a resistor 49 to the central point of the secondary of the transformer 44 from the negative terminal of a source 18 of potential, the positive terminal of which is grounded.

The anodes 18 and H of the devices I6 and I1 are connected together through the primary of an interstage transformer 5I, which is shunted by a non-linear resistor 52, which is similar to the resistor 41. This resistor 52 is effectively in shunt to the tuned circuit which includes the secondary of transformer 5|. The central point of the primary of the transformer 5| is supplied with suitable positive potential through a resistor 53 and a source 14 of potential, the negative terminal of which is grounded. The central point is bypassed for signal frequencies to the cathodes of the devices I8 and I1 at ground by a condenser. 54. The second, or screen,'grids 12 and 13 of the devices I3 and I1 are connected together. They are by-passed to the cathode of the devices I8 and I1 at ground by a condenser 58 and are supplied with a suitable positive potential through a resistor 55 from the source 14.

The resistor 52 should be chosen in the same way as the resistor 41. That is, its coefficient a should be as small as possible and its resistance in the presence of low voltages should be of the order of impedance of the output circuit of the discharge devices I8 and I1. By such a choice of the resistors 41 and "there is a minimum amount of energy shunted from the receiver by the resistors when it is amplifying small voltages such as those produced by the sound head from reflected waves, and there is a maximum amount of energy shunted from the receiver in the presence of high voltages such as those produced by the transmitter during its operation.

It is, of course, apparent that additional stages of amplification similar to that just described may be provided; each including a resistor 52.

The receiver contains an additional stage of amplification comprising the discharge devices I8 and I9 which, in addition to amplifying, also perform the function of reducing the frequency of the waves being amplified in order to take advantage of greater selectivity possible in lower frequency circuits. This lowering of the frequency is produced by a heterodyning action between the waves transmitted from the transformer 5| and waves produced by an oscillator including an election discharge device 83. The first, or control, grid I III of the discharge device 83 is connected through a grid leak resistor 84 to the cathode. The resistor 84 is connected in shunt to a portion of an inductance 85 through blocking condensers 88 and 81. The inductance 85 is connected in shunt to a condenser 88 to form an oscillating circuit and the end of this circuit opposite to the control grid IOI is connected to the second grid I02 of device 83. The central point of the inductance 85 is supplied through a resistor 89 from a suitable source 3 of positive potential. The third grid of the device 83 is connected directly to its cathode and an anode I03 thereof is supplied through the primary 90 of a transformer from the source I I3. The secondary 9| of this transformer is connected between the center point of the secondary 92 of the transformer 5| and a resistor 93. The transformer secondary 92 is shunted by a condenser 94 to form an oscillating circuit whose ends are connected respectively to the first grids I04 and I05 of the devices I8 and I8. A suitable negative bias potential for these first grids is supplied through the resistor 93 from a source 19.

The transmitter and the first amplifying stage of the receiver are tuned to some suitable high frequency, such, for example, as 30 kilocycles. The heterodyne oscillator comprising the device 83 operates at a frequency somewhat different from the transmitter frequency, so that the devices I8 and I9 by heterodyning action produce a wave whose frequency is the difference of the transmitter frequency and the frequency of the oscillator including device 83. This heterodyne wave may, for example, have a frequency of 5000 cycles.

The connection between the transformer secondary 9| and the resistor 93 is by-passed by a condenser 95 to the cathodes of the devices I 8 and I9, which are grounded. The anodes I and I01 of the devices I8 and I9 are connected together through a tuned circuit comprising the primary of an iron core transformer 51 shunted by a condenser 95. The center point of the primar of the transformer 51 is by-passed to ground through a condenser 91 and is supplied through a resistor 98 from the source II3 of positive potential. The second grids, I08 and I09 of the devices I8 and I9, are by-passed to ground through a condenser 99 and are supplied through a resistor I00 from the source H3. The secondary N0 of the transformer 51 transmits energy which excites a glow lamp 20, which produces light whenever an impulse is received and amplified by the receiver.

It is apparent that additional stages of amplification similar to that including the devices I8 and I9 may be provided to obtain increased amplification and selectivity. Such additional stages are represented by the rectangle I20.

In operation the cam 82 rotates and allows the transmitter to produce a succession of brief wave trains, each of which acts in the sound head 80 to produce a short pulse of sound which is transmitted to and reflected from the ocean floor 8 I. Depending on the distance between the sound head 80 and the ocean floor 8i, and on certain other factors which are well known, such as the temperature and composition of the sea water, the sound wave reflected by the ocean floor 8| returns to the sound head 80 after a definite interval of time. The resistors 41 and 52 during the transmission of each brief wave train have a. low resistance so that the decay periods of the oscillating circuits of the receiver are much shorter than the interval of time between transmission and reception by the sound head 80. Therefore, when the reflected wave acts on the sound head 80 to produce a small voltage, the oscillatory circuits in the receiver are unexcited and are capable of excitation by such reflected waves. After amplification by the devices I6 and I1, and heterodyning and further amplification by the devices 83, I8 and I9, each brief wave train energizes the glow tube 20.

The interval between excitation of the glow tube 20 by a pulse produced by the transmitter and a pulse received by the sound head 80. as amplified by the receiver, may be measured by any desired means. Such means form no part of the present invention and may, for example, comprise a stroboscopic disc turned by the cam 82 and through which light from the glow tube 20 may be perceived in any position of the disc. Such a stroboscopic device is represented in the drawing as a disc III turned in synchronism with the cam 82 and provided with a radial slot IIZ through which light from the glow tube 20 may be seen.

The transmitter in applying a succession of brief wave trains to the sound head 80 energizes the receiver with voltages much larger than those applied to the receiver by the sound head due to reception of wave trains reflected from distant surfaces. Since the receiver is made sufilciently sensitive to respond well to the reflected wave trains, were it not for our invention, it would be considerably overloaded by wave train applied by the transmitter. The tuned circuits 44, 48 and 92, 94 and others, if such be employed, would be highly excited by these outgoing impulses and by reason of the persistence of oscillation would be likely to remain excited when the reflected wave is received. The resistors 41 and 52, as set forth above, have the characteristic that their resistance is smaller when the voltage applied thereacross is larger. When the resistance of the resistor 41 is low during transmission of outgoing impulses, a large portion of the voltage of such impulses is distributed on condensers 45 and 46, thereby reducing the portion applied to the tuned circuit, 44, 48. In other words, the condensers 45 and 46 decouple the tuned circuit 44, 48 and the receiver from the sound head and the transmitter during operation of the transmitter. The resistor 41 due to its low value highly damps the circuit 44, 48 and the oscillations which tend to persist therein after termination of the impulses, and upon cessation of such oscillations the resistance of the resistor 41 is restored to a ve y high value. Resistor 52, and other similar resistors if employed, of course, operate in the same way. The receiver then is in readiness to respond with its full sensitivity to the same impulse when received after reflection from a distant surface.

In order that the sensitivity of the receiver be high in the presence of reflected signals picked up by the sound head 80, all impedances connected in shunt to the wires I5, and hence in shunt to the receiver, should be of very high value while the transmitter is not operating, so that energy is not shunted from the receiver. The resistance of the resistors 41 and 52 is instantaneously high upon disappearance of the high voltage signal direct from the transmitter. The control electrode bias provided for the discharge devices l2 and I3 assures that the impedance presented to the signal channel by the transmitter, as measured between the wires l5, when it is not operating, is of a high value, which is in fact comparable with that of the resistor 41. The provision of proper bias for the control electrodes of the devices I2 and I3, which maintains those devices in substantially non-conducting condition except when the oscillator transmits signals, makes possible the attainment of this high impedance. It is, of course, possible to use other types of tubes instead of the triodes l2 and I3 and obtain operation such that the output impedance remains high even though the discharge current is not cut off in the absence of signals. Such tubes as pentodes, for example, can be operated to have such high impedance.

Although this apparatus has been described as particularly useful in submarine signaling systems, it is to be understood that its use is not so limited. It is in fact useful in any situation where a, transmitter and receiver must operate at the same frequency on the same channel.

While we have shown a particular embodiment of our invention, it will, of course, be understood that we do not wish to be limited thereto, since different modifications may be made both in the circuit arrangement and in the instrumentalities employed, and we aim by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of he United States is:

1. In a signal apparatus, the combination of a translating device, a transmitter and a receiver connected thereto, said transmitter comprising a signal output stage permanently connected to said translating device and an exciting stage keyed to supply impulses through said output stage to said translating device to be emitted thereby and to be received by said receiver from said translating device after reflection from a suriace, saidreceiver including an impulse detecting device and an oscillatory circuit, means to supply impulses received in said translating device through said oscillatory circuit to said detecting device, said signal output stage having impulses passing from aid translating device to said oscillatory circuit impressed thereon by reason or the permanent connection of said output stage to said translating device, means onerative except when said transmitter is supply- .ing impulse to said translating device for maintaining the impedance 01' said output stage sufflciently high to eliminate any substantial diversion of received energy from said oscillatory circuit by said transmitter, said oscillatory circuit being subject to excitation into oscillation by impulses supplied by said transmitter to said translating device, and means eflective during operation or said transmitter to reduce the effectiveness of said impulse supplying means to supply impulses to said oscillatory circuit and to damp oscillation of said oscillatory circuit during the interval between emission and reception of an impulse sufllciently that the response of said detecting apparatus to said impulse is not materially impaired by previous excitation of said circuit by the same impulse when transmitted.

2. In a signal apparatus, a translating device, a receiver, a transmitter permanently connected to said translating device and having an output arranged to supply to said translating device impulses to be emitted thereby and to be received by said receiver from said translating device after reflection from a surface, said receiver including an oscillatory circuit, means to supply impulses received in said translating device to said oscillatory circuit, said circuit being subject to excitation into oscillation by impulses supplied by said transmitter to said translating device, means to reduce the effectiveness of said impulse supplying means during operation or said transmitter and to damp oscillation 01' said oscillatory circuit during the interval between emission and reception of an impulse sufliciently citation of said circuit by the same impulse when transmitted, and means operative except when said transmitter is supplying impulses to said translating device to increase the impedance of the output of said transmitter sumciently high to render said transmitter substantially ineffective during the period of reception of such impulses, whereby the energy of received impulses is not substantially dissipated in said transmitter.

3. In a signal apparatus, the combination of a translating device, a transmitter and a receiver connected therewith, said transmitter being permanently connected to said translating device and arranged to supply to-said translating device impulses to be emitted thereby and to be received by said receiver from said translating device after reflection from a surface, said receiver including an oscillatory circuit in which impulses are received from said translating device, said circuit being subject to excitation by an impulse from said transmitter during transmission of such an impulse, means for coupling said oscillatory circuit in shunt to said translating device and said transmitter, means for increasing coupling through said coupling means between said receiver and translating device during reception of an impulse from said translating device, means operative except when said transmitter is supplying impulses to said translating device for increasing the impedance of the output of said transmitter sufliciently high to eliminate any substantial diversion of received energy from said translating device by said transmitter, thereby rendering said transmitter substantially ineffective to supply impulses durin the period of reception of reflection impulses by said translating device, and mean for decreasing coupling through said coupling means in the presence of an impulse received directly from said transmitter, said last means being efiective to damp waves excited in said oscillatory circuit by an impulse from said transmitter before said impulse i returned from said surface.

' DONALD E. WA'I'I'S.

PAUL C. GARDINER. 

